1. Field of the Invention
This invention relates to an EL device employing electrical luminescence, namely EL, more particularly to an EL device having a luminescent layer, comprising a thin film of a mixture of at least one electroluminescent organic compound and at least one organic compound different in electronegativity from said organic compound where the compounds are arranged in a high order of molecular orientation, and further to an EL device, having a luminescent layer of a double-layer structure, each layer comprising a thin film of at least one electroluminescent organic compound different in electronegativity relatively to the adjacent layer.
2. Description of the Prior Art
EL devices of the prior art have a luminescent layer comprising a luminescent matrix of ZnS containing Mn or Cu or ReF.sub.3 (Re represents a rare earth ion) as an activator, and can be classified into the powder type EL and the thin layer type EL according to the difference in basic structure of said luminescent layer.
Of the devices practically applied, thin layer EL devices give generally higher luminance than the powder type EL, but thin layer EL devices, having a luminescent layer formed by vapor deposition of a luminescent matrix on the substrate, cannot easily be manufactured into a large area device and also have the disadvantage of very high production cost. Accordingly, powder type EL comprising a luminescent matrix, namely ZnS, dispersed in an organic binder, which is most suitable for mass production with low cost, namely about a few tenths of the cost of the thin layer type device, is now attracting attention. Generally speaking, in electrical luminescence, the luminescent characteristic will be improved as the luminescent layer is made thinner. However, in the case of said powder type EL, in which the luminescent matrix consists of discontinuous powder, pinholes are liable to be formed when the luminescent layer is made thinner, and therefore the layer cannot easily be made sufficiently thin, thus involving a serious drawback that no satisfactory luminance characteristic can be obtained. Further, in recent years, an improved device having an intermediate dielectric layer comprising a vinylidene fluoride polymer arranged within the luminescent layer of said powder type EL has been disclosed in Japanese Laid-open Patent Publication No. 172891/1983, but no satisfactory performance with respect to luminance, power consumption, etc. has yet been obtained. On the other hand, quite recently, researches and developments are actively trying to obtain new optical and electronics materials by controlling chemical structures or orderly structures of organic materials, and organic materials comparable with or surpassing metals or inorganic materials have been reported, including EC element, piezoelectric element, pyroelectric element, non-linear optical element, ferroelectric liquid crystal, etc. Thus, while it has been desired to develop a functional organic material as the new functional material surpassing inorganic materials, an EL device having a built-up film of monomolecular layers of an anthracene derivative or a pyrene derivative having a hydrophilic group and a hydrophobic group within the molecule has been proposed in Japanese Laid-open Patent Publication No. 35587/1977. However, those EL devices have not yet attained satisfactory performance as a practical EL device with respect to luminance, power consumption, etc. Further, in the case of said organic EL device, the denisty of carrier electrons or holes is very low, resulting in the very low excitation probability of the functional molecules through recombination of carriers, etc., whereby no efficient luminescence can be expected.